[listenallyall]

Sony, unfortunately, has no partnerships with any carriers, no place to go to repair a phone, no marketing on the US, all making it nearly impossible to sell any phones. Their pricing strategy is quite bizarre as well.

Samsung is the dominant Android player, for a variety of reasons. Pixel and OnePlus (and Samsung and Apple) make a lot of extra money by charging $100/$200 to boost from 128gb to 256 or 512 but that strategy doesn't differentiate them and definitely doesn't make Samsung loyalists switch.

You cannot state that adding an SD slot wouldn't improve market share, because there are no premium competitors who do, the hypothesis is untested.